Screening Of Efficient Denitrifying Bacteria And Their Applications In Wastewater Denitrification Process

Nitrogen and phosphorus pollutants are the main drivers of eutrophication in the marine,resulting in destroying the ecosystem.Biological nitrogen removal is regarded as the most efficient and economically feasible method available for the removal of ammonia from wastewater.The biological nitrogen removal processes involve ammonification,nitrification,and denitrification,and denitrification is the crucial stage that determines the efficiency of nitrogen removal.Although some autotrophic denitrification bacteria have been used in denitrification,the efficiency of denitrification depends on the heterotrophic denitrifying bacteria.Heterotrophic denitrifying bacteria use the organic carbon source as the electron donor and then deliver the electron to nitrate,resulting in the nitrate being reduced into nitrogen gas.All the known denitrifying bacteria exhibit a low rate of removal of nitrogen and require abundant organic carbon sources.Therefore,it is necessary to explore efficient denitrifying bacteria that require less organic carbon sources.The main results are as follows:(1)Comamonas sp.(named DB-1),Stenotrophomonas sp.(named DB-2),Pseudomonas sp.(named DB-3),and Acinetobacter sp.(named DB-4)were isolated as denitrifying bacteria based on BTB separation.Here,Comamonas sp.(DB-1)and Stenotrophomonas sp.(DB-2)were identified as denitrifying bacteria for the first time.(2)The characterizations of the denitrification of these four denitrifying bacteria were investigated carefully.The results showed that the denitrification rate of DB-1 was 50mg/L·h,it could perform denitrification in a broad range of p H,and up to 80% total nitrogen was removed at p H 7.0-8.0.Moreover,DB-1 could utilize sucrose as the electron donor to complete the denitrification,and the ratio of removal of total nitrogen could reach 80 % at C/ N of 7.Therefore,DB-1 strain could be used for the denitrification of various polluted water.At 20-37 ℃,the denitrification ability of DB-1 increased with the increase in temperature.DB-2 could remove 90% of total nitrogen at 37 ℃.DB-4 removed 60% of the total nitrogen at p H 6.0-8.0,and it could remove 80% of total nitrogen at 25 ℃.The results showed that DB-4 strain has a strong denitrification ability at low temperatures and a wide p H range.(3)The production of lyophilized DB-1 and liquid formulation of DB-1 was also investigated.DB-1 was cultured in a 50 L fermentation tank at initial vvm= 0.2,30℃,and p H= 7.0-8.0,and the cells were harvested when the OD600 up to 1.95,which contained about 4.0 billion CFU/ m L.The lyophilized samples contained 2 1 billion CFU/when the cells were prepared as lyophilized cells.Meanwhile,if 1 ‰ sodium benzoate was added to the fermented broth and stored at 4 ℃ for 90 days,the survival rate of DB-1 was 60%.(4)DB-1 had strong denitrification in both the mini-bioreactor fermentation system and pilot-scale reactor.The DB-1 liquid formulation was further used in the denitrification of wastewater in the reactor(1L/5L)and pilot-scale reactor(1000 m3/d).DB-1 treatment could remove 20 % more nitrate than the control(using activated sludge)after 24 h when the concentration of Na NO3 at 20 mg/L;and the DB-1 treatment could remove 10% more nitrate than the control after 48 h when the concentration of Na NO3 at 40 mg/L.When DB-1was applied in the pilot-scale reactor,the ratio of nitrogen removal was above 95,but the activated sludge treated process only removed 60%-85% of the total nitrogen.In conclusion,the low-cost lyophilized DB-1 and liquid formulation of DB-1 showed strong denitrification of wastewater in a pilot scale.The results indicated that DB-1 has wide application in the treatments of wastewater,and it also provides strong support for the biological nitrogen removal in the wastewater treatment plant.